1. Field of the Invention
Exemplary aspects of the present disclosure generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photoconductive drum); an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
The image forming apparatus using an intermediate transfer method employs a belt-type intermediate transfer member (hereinafter referred to simply as intermediate transfer belt) formed into an endless loop that contacts the photoconductive drum, forming a primary transfer nip therebetween. In the primary transfer nip, a toner image formed on the photoconductive drum is transferred primarily onto the intermediate transfer belt. This process is known as “primary transfer process”.
A secondary transfer roller contacts the intermediate transfer belt, forming a secondary transfer nip, so that the toner image on the intermediate transfer belt is secondarily transferred onto a recording medium in a process known as “secondary transfer process”. A secondary transfer counter roller is disposed inside the loop formed by the intermediate transfer belt, facing the secondary transfer roller with the intermediate transfer belt interposed therebetween.
The secondary transfer counter roller disposed inside the loop of the intermediate transfer belt is grounded; whereas, the secondary transfer roller disposed outside the loop is supplied with a secondary transfer bias. With this configuration, a secondary transfer electric field that electrostatically transfers the toner image from the secondary transfer counter roller side to secondary transfer roller side is formed. The toner image on the intermediate transfer belt is transferred secondarily onto a recording medium supplied to the secondary transfer nip in appropriate timing such that the recording medium is aligned with the toner image formed on the intermediate transfer belt.
When using a recording medium having a coarse surface such as Japanese paper, a pattern of light and dark according to the surface condition of the recording medium appears in an output image. More specifically, toner is transferred poorly to recessed portions on the surface of the recording medium. As a result, the density of toner at the recessed portions is less than that of projecting portions. In view of the above, in a known image forming apparatus, a secondary bias composed only of a direct current voltage is not used, but a bias in which a direct current voltage is superimposed on an alternating current voltage is supplied, thereby preventing the pattern of light and dark, as compared with supplying only the direct current voltage.
In general, known image forming apparatuses produce a test image known as a toner pattern to achieve target image quality. For example, the toner pattern is formed on the intermediate transfer belt at specific times for example, between successive recording media sheets. Then, an optical detector detects the toner pattern. Based on the result detected by the optical detector, image quality control such as adjustment of the density of the image and correction of color drift are performed. Furthermore, the toner pattern is formed between successive recording media sheets to replace spent toner in a developing device with fresh toner to maintain imaging quality.
When performing the image quality control, the secondary transfer roller is separated from the intermediate transfer belt so that the toner pattern formed on the intermediate transfer belt is not transferred onto a recording medium. Instead, the toner pattern is removed by a cleaning device, for example, a cleaning blade.
The cleaning device needs to adequately remove toner of the toner pattern from the intermediate transfer belt. Otherwise, the toner remaining on the intermediate transfer belt may stick to a successive recording medium. However, when a large amount of toner is adhered to the toner pattern on the intermediate transfer belt, it is difficult to remove the toner from the intermediate transfer belt thoroughly.
Similarly, in an image forming apparatus using a direct transfer method in which the toner image is directly transferred from the photoconductive drum to a recording medium, the toner in the toner pattern formed on the photoconductive drum may not be removed thoroughly.
In view of the above, there is demand for an image forming apparatus that is capable of adequately removing a toner pattern.